In the future, an unnamed marine (known as the "Doom marine" or "Doom guy") is posted to a dead-end assignment on Mars after assaulting a superior officer who ordered his unit to fire on civilians. The Union Aerospace Corporation, which operates radioactive waste facilities there, allows the military to conduct secret teleportation experiments that go terribly wrong. A base on Phobos urgently requests military support, while Deimos disappears entirely, and the marine joins a combat force to secure Phobos. He waits at the perimeter as ordered while the entire assault team is wiped out. With no way off the moon, and armed with only a pistol, he enters the base intent on revenge.